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Remove The Catalytic Converter Or Keep It?


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#1 j.gerbes

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Posted 10 January 2018 - 08:00 PM

Hey all, I'm upgrading the stock exhaust on my SPI Mini to a new Maniflow and am having a hard time deciding whether to keep the catalytic converter or remove it.

 

Here in New Zealand we don't have any emissions regulations (the only rule is that the car can't blow black smoke - seriously), so the catalytic converter is optional.

 

I'm planning to go with a Stage II LCB manifold and a twin box side exit exhaust, either with or without the catalytic converter.

 

What are your thoughts? Would it perform better without the cat? Smell worse? Sound better or worse?



#2 Sprocket

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Posted 10 January 2018 - 08:29 PM

I the regulations in NZ do not require a cat to be present, or the prescribed emissions limits are such that it doesn't need it, then there is no reason to keep it other than your own personal feelings on the whole environmental impact thing.

 

The exhaust will smell noticeably different, but with the SPI so long as the system is functioning tip top, it won't be eye wateringly bad as some carbs seem to be. The exhaust tone will be noticeably different, maybe not so much louder, but will depend on your choice of mid box/ back box. As for performance, it is debatable whether any noticeable difference in power is seen with standard to mild tunes (Yet to see back to back dyno results to say one way or the other). I kept the standard cat on my 1400SPi and it pushed 99hp at the red line fuel cut. Perhaps it would have been more without the cat, but in the main, if you can achieve 99hp with the cat, it's not the most restrictive part of the overall system.



#3 absx2

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Posted 10 January 2018 - 08:34 PM

The cat seems to reduce the boom noise from within the cabin or should I say I noticed more boom after removing one and fitting a link pipe.  



#4 ukcooper

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Posted 10 January 2018 - 08:53 PM

cat makes it quitter , but getting it set up for clearance is a pain in the ass

#5 j.gerbes

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Posted 10 January 2018 - 09:10 PM

Thanks all for your replies!

 

I would be going with a twin box Maniflow such as this one.

 

Ground clearance is not too much of an issue but it would be nice to have more of it (I have hit the cat a couple of times over speed bumps).

 

What I am most concerned about is the sound that the car will make while warming up (with the 'choke' on) and while travelling at motorway speeds. Does it drone without a cat?

 

@absx2, what sort of exhaust do you have installed? Is it standard or aftermarket, single box or twin?



#6 absx2

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Posted 10 January 2018 - 09:55 PM

 Does it drone without a cat?

 

@absx2, what sort of exhaust do you have installed? Is it standard or aftermarket, single box or twin?

 Yes, most do and some don`t but minis aren't known for quiet cabins :) Injection cars seem better as they are more likely to be running in tune due to the engine management.

 

I removed the cat on a standard system and noticed the noise increase.  I have used an RC40 and a Maniflow on the same car, both twin box and both increased the cabin noise a bit. The main problem is around 4k revs and on overrun at higher revs but its no big deal.

 

The maniflow system is very well built and lasts much longer than an Rc40 based on my 22 years of using them and personally I would choose the maniflow system every time.  



#7 Zach P-D

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Posted 12 January 2018 - 10:12 PM

removed my CAT and replaced with a single link pipe from the back of the LCB to my center exit back box, sounds lovely and clearance is rather good

#8 brivinci

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Posted 22 January 2018 - 09:10 PM

I removed my CAT on my 94 SPi was I am in the US and it was not needed. I also figured I'd keep it just in case...and good thing I did because the engine was consuming a ton of oil and probably would have ruined the CAT. 

 

I am running a full Maniflow system, from LCB to back. I have both a single box and a twin box cat-back systems. I replaced the CAT with their link pipe. You really dont gain much clearance as the link pipe uses the same flanges and mounting location. I guess even a little more clearance is better then nothing.

 

Interesting, I should reinstall the CAT and see how it feels/sounds. I went from a single box to the twin box but the cabin noise is high. In colder weather, with windows rolled up, you just hear that "booming" inside. You really dont hear the actual exhaust note. 

 

I think Calver did a test with and without the CAT and there was only a very slight gain, and that was only at the extreme top of the rev range. The stock CAT flowed very well.



#9 Steve220

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Posted 23 January 2018 - 04:28 PM

If you add a straight pipe instead of the cat, your car will sound like a fart in a dustbin. I would suggest getting a silenced pipe to fit instead.

#10 j.gerbes

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Posted 23 January 2018 - 08:48 PM

If you add a straight pipe instead of the cat, your car will sound like a fart in a dustbin. I would suggest getting a silenced pipe to fit instead.

Haha I definitely don't want that!

 

I have decided to keep the cat for the moment. The benefits of removing it seem small as performance gains sound marginal and I haven't experienced a clearance issue yet.

 

I'm going to replace the exhaust from the cat-back with a Mainflow twin box system



#11 brivinci

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Posted 23 January 2018 - 10:42 PM

I really like the Maniflow stuff. I think you will be pleased. Now I REALLY think I might refit my cat and see how it effects the overall sound of my car. I can't remember what it was like with the cat and the single box setup but it seems a lot louder inside the car now. 



#12 j.gerbes

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Posted 24 January 2018 - 02:33 AM

I really like the Maniflow stuff. I think you will be pleased. Now I REALLY think I might refit my cat and see how it effects the overall sound of my car. I can't remember what it was like with the cat and the single box setup but it seems a lot louder inside the car now. 

Please let me know how it goes! I removed the cat from my Audi a while ago. Every morning I start it up cold I regret that decision (as do my neighbors).



#13 brivinci

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Posted 26 January 2018 - 08:22 PM

If you add a straight pipe instead of the cat, your car will sound like a fart in a dustbin. I would suggest getting a silenced pipe to fit instead.

Thinking more about this, I have heard this comment a few times over the years. Its a little confusing...or maybe its just me BUT if this was the case, wouldn't that mean that all pre-cat minis sounds like a fart in a dustbin??



#14 Steve220

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Posted 26 January 2018 - 09:09 PM

If you add a straight pipe instead of the cat, your car will sound like a fart in a dustbin. I would suggest getting a silenced pipe to fit instead.

Thinking more about this, I have heard this comment a few times over the years. Its a little confusing...or maybe its just me BUT if this was the case, wouldn't that mean that all pre-cat minis sounds like a fart in a dustbin??

Haha! Good point! Don't they usually have 2 baffles though?

#15 Sprocket

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Posted 26 January 2018 - 10:27 PM

I've got a turbo, a sports cat, a mid section silencer and a rear section silencer, all in 2.25" and it still booms in the cabin around 4000rpm. Its the same boom whether on throttle or on overrun (no fuel, high manifold depression) so its not really got anything to do with the exhaust. The exhaust volume is low. Its tone is low.

The gearbox is noisier :D


Edited by Sprocket, 26 January 2018 - 10:38 PM.





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